Right back to square one.

swest wrote: Could be fuel starvation. Have you tried running it on prime? Get a can of carb/choke cleaner and spray through the passages. The pilots are very small so a guitar string of strand off a wire brush should go through them to make sure they're clear. Don't hit rubber parts with the spray. Braggarts aside you may have gotten a very nice bike from a guy that was ether too stupid or cheap to get it running right. :whistle: A valve adjustment check should be done before jetting the carbs.
Steve

Steve hit the nail on the head. This morning I drained the fuel, filled up with premium, and turned the petcock to prime. Ran like a champ for about 80 miles. However, it sounds like im still chasing a vacuum leak if its running good with the petcock on prime?

There are two vent ports on the carbs too, on carbs #2 & #4, purple lines, bottom picture.
There should be a length of hose on each, either coming up and over the air box, or into the air box:

Mine sit on top of the box. I don't think I would want them in the box. You need to rebuild the petcock. Your leak could be there or the carb holders are leaking. It's hard to tell. I got new ones and everything changed.
Steve

Is there an easy way to check for and find a leak in the carb holders? Also, do you have a link or part number for the specific rebuild kit I would need

swest wrote: Mine sit on top of the box. I don't think I would want them in the box. You need to rebuild the petcock. Your leak could be there or the carb holders are leaking. It's hard to tell. I got new ones and everything changed.
Steve

I resealed my old ones with :ohmy: Permatex, it worked for a while. I bought some from here.
www.diablocycle.com/Carburetor-c-67/
Pics of the carbs could help.
jetsrus.com/index.html
Another place for parts.
jbmindustries.com/
Careful buying on eBay. Some sellers don't care if you get the right parts, all they want is your MONEY.
Steve

Carb kits can be a waste of money, since there's usually extra parts to cover a range of models.
aftermarket jet needles sometimes have the wrong taper & the jet sizes may not match the mikuni jets.

I would remove the carburetors from the motorcycle, then remove the float bowls & clean the little parts. then decide what you need. you might be able to read the numbers on the main jets. mine are 92.5. yours probably have a different number. I don't know if the pilot jets have numbers on them. stock is #15.

HF metric nitrile o-ring kit. or viton rubber kit. or eebbaayy. Z1Enterprises.com. o-rings. gaskets. etc.
you might be able to rejuvenate the top gaskets by soaking w LW silicone spray.

Am I safe to go ahead and ride the bike just setting the petcock to prime? Riding season is about to start and I don't have the time at the moment for some of these projects. I'm hoping I can just ride it till the weather gets cold then this winter I will check valve clearance/replace valve cover gasket and also pull/clean/rebuild the carbs

You need to check the valves no matter what.
Steve

Yeah kinda the answer I expected. Looks like I'll be ordering a gasket knowing my impatient butt will ruin the original. Any good walk throughs on the forum? Did a search and could find anything specific

The carb holders can be checked for leaks by spraying carb cleaner around them while the bike is idling.
If the rpms change, there is a leak.

KZ650 specific maintenance procedures can be found at kz650.info, link in my signature.